1. Field of the Invention
The present invention relates to a wafer surface measuring apparatus capable of detecting foreign substances, such as particles or the like, or fine defects existing on the surface of a semiconductor wafer by using light scattering.
Priority is claimed on Japanese Patent Application No. 2009-029952, filed Feb. 12, 2009, the content of which is incorporated herein by reference.
2. Description of the Related Art
Up to now, a wafer surface measuring apparatus of a laser scattering type has been known as an apparatus for detecting foreign substances, such as particles or the like, or fine defects existing on the surface of a semiconductor wafer (hereinafter, referred to as a wafer). The wafer surface measuring apparatus can perform detection of particles or defects by irradiating a laser beam on the wafer which is loaded on a measuring stage and rotated at high speed and detecting scattered light from the wafer surface. Prior art is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2008-267827.
In such a wafer surface measuring apparatus, if carrying of the wafer to the measuring stage is manually performed, working efficiency is low, and the possibility of contamination of the wafer, such as by particle adhesion, is high, because of the interposition of manual working. Consequently, such a wafer surface measuring apparatus is generally located in a box-shaped clean room. The wafer surface measuring apparatus is configured to discharge the wafer from a cassette, which is carried to the clean room, by using an arm, and then carry the wafer to the measuring stage.
Meanwhile, when the wafer is carried by the arm, only the outer edge of the wafer is supported by the arm in order to prevent flaws from being produced on the rear surface thereof, or particles from adhering to the rear surface, since the finishing of the front and rear surfaces of the wafer is to a mirror surface. In the state in which the wafer is loaded on the measuring stage, only the outer edge thereof is supported, so that the rear surface of the wafer does not come in contact with the stage surface.
In the case in which the wafer is loaded on the measuring stage, the center portion of the wafer is bent downward by its own weight. Therefore, when the wafer is measured, the wafer surface measuring apparatus of the related art ejects gas for upper wafer from a center portion of the stage surface which loads the wafer, so that the bending of the wafer is corrected by pressure of the gas (For example, see Japanese Unexamined Patent Application Publication No. 2003-303878). As a result, the non-contact state between the rear surface of the wafer and the stage surface of the measuring stage is maintained and flatness of the surface of the wafer is maintained, thereby performing the measurement with high accuracy.
The above-described wafer surface measuring apparatus can deal with a wafer having a diameter of 300 mm or less at present, but it will be necessary to deal with a wafer having a diameter of 450 mm in the future. However, in the case of a large-diameter wafer, since bending of the center portion of the wafer due to its own weight is increased when the wafer is loaded on the measuring stage, a problem may happen in that the center portion of the wafer comes into contact with the stage surface before the outer edge of the wafer is supported. Even though the diameter of the wafer is 300 mm like the past, if the thickness of the wafer is thin, the bending amount increases. Thus, the wafer comes in contact with the stage.
It is conceivable that contact between the wafer and the stage can be avoided by increasing the space between the rear surface of the wafer and the stage surface. In this instance, there is a problem in that since turbulent flow is produced when the gas ejected from the center portion of the stage passes through the gap between the rear surface of the wafer and the stage surface, the wafer is vibrated or particles are generated.
The invention has been made to take the above problem into consideration, and an object of the invention is to provide a wafer surface measuring apparatus capable of supporting a wafer having a large diameter or thin thickness on a measuring stage in a state of non-contact between a rear surface of the wafer and the measuring stage.